At least 75 companies receive people’s precise location data from hundreds of apps whose users enable location services for benefits such as weather alerts, The New York Times found. The companies use, store or sell the information to help advertisers, investment firms and others.

You can head off much of the tracking on your own device by spending a few minutes changing settings. The information below applies primarily to people in the United States.

How can I tell if apps are sharing my location?

It’s difficult to know for sure whether location data companies are tracking your phone. Any app that collects location data may share your information with other companies, as long as it mentions that somewhere in its privacy policy.

But the language in those policies can be dense, confusing or outright misleading. Apps that funnel location details to help hedge funds, for instance, have told users their data would be used for market analysis — or simply for “business purposes.”

Which apps gather and share location?

There isn’t a definitive list. Our tests identified instances of certain apps collecting precise location data and passing it to other companies in the moment. But apps can also gather and save the data, and not sell it until later — something tests wouldn’t catch. Your best bet is to check your device to see which apps have permission to get your location in the first place.

The apps most popular among data companies are those that offer services keyed to people’s whereabouts — including weather, transit, travel, shopping deals and dating — because users are more likely to enable location services on them.

How do I stop location tracking on iOS?

Some apps have internal settings where you can indicate that you don’t want your location used for targeted advertising or other purposes. But the easiest method is to go through your device’s main privacy menu.

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First, open Settings and select Privacy, which has a blue icon with a white hand.

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Then select Location Services, which is at the top and has a little arrow.

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You’ll see a list of apps, along with the location setting for each. Tap on apps you want to adjust. Selecting “Never” blocks tracking by that app.

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The option “While Using the App” ensures that the app gets location only while in use. Choosing “Always,” allows the app to get location data even when not in use.

In the device’s privacy settings, apps provide brief explanations of how they will use location data. Do not rely on these descriptions to tell you whether the location data will be shared or sold. The Times found that many of these descriptions are incomplete and often don’t mention that the data will be shared.

If you want to disable location tracking entirely, toggle the “Location Services" setting to off. With location services switched off entirely, you may not be able to use certain services, such as finding yourself on a map.

If you have apps you no longer use, you may want to delete them from your device.

How do I stop it on Android?

These instructions are for recent Android phones; Google provides more instructions here.

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First, open the Settings on your phone. On the main settings page, tap “Security & location.”

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On the next screen, tap Location, which can be found in the Privacy section.

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On the Location screen, tap “App-level permissions.”

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You’ll see a list of apps. To turn off location for an app, slide the toggle to the left.

Unlike iPhones, Android phones don’t allow you to restrict an app’s access to your location to just the moments when you’re using it. Any app on Android that has your permission to track your location can receive the data even when you’re not using it. In newer versions of Android, the collection of this data is limited to “a few times an hour,” Google says.

To disable location services altogether, switch off “Use location,” within the same Location settings described above. Google’s instructions are here.

If you don’t enable location services at all, you may not be able to use certain services, like finding yourself on a map. If you want to be able to switch periodically between having location services on and off, you can create a Quick Setting. To see your Quick Settings, swipe down from the top of your screen and tap the little pencil to edit.

If you have apps you no longer use, you may want to delete them from your phone.

Can I delete my location data from these databases?

The location data industry benefits from lack of regulation and little transparency, making it extremely difficult to get access to or delete this data. Your information can also be spread among many companies. And most of them store location data attached not to a person’s name or phone number, but to an ID number, so it may be cumbersome for them to identify your data if you want to delete it — and they are under no obligation to do so.

In the European Union, people now have the legal right to request a copy of the data that companies hold about them, and to ask that it be deleted. The British data commissioner provides an explanation, here.

Google, a prominent collector of location data, lets users delete a segment of that information called their Location History. To do that, go to this page, then hit the Delete Location History button. Click it again when prompted. You can delete another segment of location data associated with your Google account by logging in and going to My Activity. Then click on Activity Controls and turn off Web & App Activity.

Jennifer Valentino-DeVries is an investigative reporter covering technology and public policy. @jenvalentino

A version of this article appears in print on , on Page A21 of the New York edition with the headline: How to Stop Your Smartphone Apps From Tracking Your Location. Order Reprints | Today’s Paper | Subscribe